The invention relates to fuel cells. More particularly, the invention relates to fuel cell electrodes. Even more particularly, the invention relates to cathode materials for fuel cell electrodes.
Polymer electrolyte fuel cells (PEFCs) based on direct methanol fuel cells (DMFCs) have attracted great interest as an alternative power source for vehicles and portable electronic devices. Factors that significantly reduce the efficiency of DMFCs include sluggish methanol oxidation at the anode, sluggish oxygen reduction reaction (ORR) at the cathode, and methanol crossover. The sluggish methanol oxidation and ORR cause a large overpotential at the anode and the cathode, respectively, thus dramatically reducing cell voltage. Methanol crossover is the permeation of methanol through the solid electrolyte membrane from the anode to the cathode, where it is oxidized. The simultaneous ORR and oxidation of methanol at the cathode lead to an additional reduction of the cathode potential and decrease in DMFC performance.
Platinum and platinum-based metal alloys are, at present, the most widely used ORR catalysts in DMFCs. However, these catalysts suffer significant loss in activity in the presence of methanol due to poisoning by methanol. Efforts have been made to develop alternative ORR catalysts other than platinum that are either inactive or sufficiently tolerant to methanol. Nano-cluster MoxRuySez and RuxSey compounds, for example, have been prepared from ruthenium carbonyl precursors.
The development of highly active, methanol tolerant cathode catalysts for ORR is one of the most important considerations in achieving high efficiency DMFCs. Therefore, what is needed is a fuel cell catalyst having adequate tolerance to methanol. What is also needed is a method of making such electrode catalysts.